This invention relates to tape transports for the traversal of magnetic tape past a recording and/or playback head and in particular to an improved tape tension sensor for use in such a transport.
In most kinds of magnetic tape recording and playback machines, magnetic tape is transported along a path defined by a plurality of guides from a supply reel of tape past a recording or playback head to a take-up reel. The tape is usually driven by a capstan engaging the tape at an appropriate location along the path, the location depending on the particular machine. In many machines, particularly although not exclusively machines adapted for the recording of television signals on magnetic tape, at least one loop of tape is formed by the guide system at a convenient location along the path of the tape. The tension of tape in this loop is sensed in order, for example, to provide servomechanical control of the speed of an associated supply or take-up reel. It will be appreciated that the capstan is the prime mover of the tape past the recording or playback head but where the reels for the tape are of substantial size, it is desirable to drive the supply and take-up reel separately from the capstan in order that the capstan need only move the tape and does not require to produce any torque for moving the supply reel. However, where the supply and take-up reels are separately driven, it is usually desirable to control their speeds servomechanically in order to maintain the tension of the tape both upstream and downstream of the capstan at a reasonably constant value.
In many arrangements, a loop of tape is engaged by a guide roller which is mounted for translational movement so that as the tension in the tape forming the loop varies, the tape guide moves accordingly. This movement may be sensed in order to provide a control for the respective take-up or supply reel.
Very many proposals have been made for measuring the tension in a tape by sensing the length of a loop of tape in order to provide a control for an associated servomechanism which regulates the tape tension. Many of these proposals are of complex construction and suffer from the considerable disadvantage that it is difficult to linearise or otherwise control the relationship between a parameter (which may be either the loop length or the tape tension) and an output signal from a transducer cooperating with the movable guide to produce an indication of the sense and magnitude of the controlling parameter.
Accordingly, it is an object of the present invention to provide an improved tape loop sensor for a tape transport.
Another object of the invention is to provide an improved tape loop sensor in which the provision of a desired relationship between a controlling parameter and the output of an associated transducer is rendered more feasible.
Another object of the invention is to provide an improved tape loop sensing arrangement including a loop sensor and a transducer of comparatively simple design for providing a signal indicative of the tape tension.